Control channel allocation method, and apparatus for same

ABSTRACT

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for performing processes in which a terminal determines control channel allocation, as well as to an apparatus for the method. The method comprises the following steps: monitoring, on a first carrier, a first search space, containing a control channel candidate set, for control channels having no carrier indication information; and monitoring, on a second carrier, a second search space, containing a control channel candidate set, for control channels having carrier indication information. If the terminal is set to monitor a plurality of control channel candidates which have the same radio network temporary identifier (RNTI), the same information size, and the same first control channel element (CCE) in the first search space and in the second search space, the control channels are received only in the first search space on the first carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/513,099 filed on Sep. 5, 2012, now U.S. Pat. No. 8,687,584 issued onApr. 1, 2014, which is the national phase of PCT InternationalApplication No. PCT/KR2011/001718 filed on Mar. 11, 2011, which claimsthe benefit of U.S. Provisional Application Nos. 61/313,083 filed onMar. 11, 2010, 61/317,235 filed on Mar. 24, 2010, 61/320,293 filed onApr. 1, 2010, 61/324,301 filed on Apr. 15, 2010, 61/326,205 filed onApr. 20, 2010 and 61/328,676 filed on Apr. 28, 2010, the entire contentsof all of the above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wireless communication system, andmore particularly to a method and apparatus for allocating a controlchannel.

Discussion of the Related Art

Wireless communication systems have been widely used to provide variouskinds of communication services such as voice or data services.Generally, a wireless communication system is a multiple access systemthat can communicate with multiple users by sharing available systemresources (bandwidth, transmission (Tx) power, and the like). A varietyof multiple access systems can be used. For example, a Code DivisionMultiple Access (CDMA) system, a Frequency Division Multiple Access(FDMA) system, a Time Division Multiple Access (TDMA) system, anOrthogonal Frequency Division Multiple Access (OFDMA) system, a SingleCarrier Frequency-Division Multiple Access (SC-FDMA) system, and thelike.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor efficiently allocating a control channel in a wireless communicationsystem supporting carrier aggregation (CA). Another object of thepresent invention is to provide a method and apparatus for overcomingambiguity/blocking capable of being generated in control channelallocation. Another object of the present invention is to provide amethod and apparatus for efficiently performing blind decoding of acontrol channel. Another object of the present invention is to provide amethod and apparatus for constructing a search space to efficientlytransmit a control channel.

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technicalobjects and other technical objects which are not mentioned herein willbe apparent from the following description to one of ordinary skill inthe art to which the present invention pertains.

The object of the present invention can be achieved by providing amethod for performing a procedure for determining control channelallocation for a control channel by a user equipment (UE) in a wirelesscommunication system, the method including monitoring a first searchspace comprising a set of control channel candidates on a first carrier,wherein the set of control channel candidates is for a control channelhaving no carrier indication information; and monitoring a second searchspace comprising a set of control channel candidates on a secondcarrier, wherein the set of control channel candidates is for a controlchannel including carrier indication information, wherein, if the userequipment (UE) is configured to monitor a plurality of control channelcandidates having the same radio network temporary identifier (RNTI),same information size and same first control channel element (CCE) inthe first and second search spaces, the control channel is capable ofbeing received only in the first search space on the first carrier.

In another aspect of the present invention, a user equipment (UE)configured to determine control channel allocation for a control channelin a wireless communication system includes a radio frequency (RF) unit;and a processor, wherein the processor monitors a first search spacecomprising a set of control channel candidates on a first carrier, theset of control channel candidates being used for a control channelhaving no carrier indication information, and monitors a second searchspace comprising a set of control channel candidates on a secondcarrier, the set of control channel candidates being used for a controlchannel including carrier indication information, wherein, if the userequipment (UE) is configured to monitor a plurality of control channelcandidates having the same radio network temporary identifier (RNTI),same information size and same first control channel element (CCE) inthe first and second search spaces, the control channel is capable ofbeing received only in the first search space on the first carrier.

In association with the plurality of control channel candidates, thecontrol channel may be capable of being received only in the firstsearch space.

If the control channel is detected in the plurality of control channelcandidates, the control channel may be considered to be received in thefirst search space.

The monitoring of the plurality of control channel candidates may becarried out assuming that the control channel is received only in thefirst search space.

The plurality of control channel candidates may be CRC(Cyclic RedundancyCheck)-scrambled with the same RNTI.

The information size may be a downlink control information (DCI) payloadsize.

The first search space may be a common search space, and the secondsearch space may be a UE-specific search space.

The control channel may be a physical downlink control channel (PDCCH),and the control channel candidate may be a PDCCH candidate.

The first carrier may be identical to the second carrier.

The plurality of control channel candidates may be generated byoverlapping of the first and second search spaces.

The method may further include receiving a subframe, wherein thesubframe includes a control region comprised of one or more contiguousorthogonal frequency division multiplexing (OFDM) symbols in a frontpart thereof, and the first search space and the second search space arepresent in the same control region.

The method may further include performing operations caused by thecontrol channel.

As is apparent from the above description, exemplary embodiments of thepresent invention have the following effects. A control channel can beefficiently allocated in a wireless communication system supportingcarrier aggregation. The embodiments of the present invention canovercome ambiguity/blocking capable of being generated when a controlchannel is allocated. The embodiments of the present invention canefficiently perform blind decoding of a control channel. The embodimentsof the present invention can efficiently construct a search space.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project (3GPP) system.

FIG. 2 exemplarily shows a resource grid of a downlink (DL) slot.

FIG. 3 exemplarily shows a downlink (DL) frame structure.

FIG. 4 is a flowchart illustrating a method for constructing a PDCCH byan eNode B.

FIG. 5 is a flowchart illustrating a process for receiving a PDCCH by auser equipment (UE).

FIG. 6 exemplarily shows an uplink (UL) subframe structure.

FIG. 7 exemplarily shows a carrier aggregation (CA) communicationsystem.

FIG. 8 exemplarily shows scheduling for use in an aggregate of multiplecarriers.

FIG. 9 exemplarily shows eNB and UE operations for use in a CIFreconfiguration section.

FIGS. 10A to 10D exemplarily show one method for overcoming ambiguityencountered in control channel reception according to one embodiment ofthe present invention.

FIG. 11 exemplarily shows another method for overcoming ambiguityencountered in control channel reception according to one embodiment ofthe present invention.

FIGS. 12 to 19 exemplarily show another method for overcoming ambiguityencountered in control channel reception according to one embodiment ofthe present invention.

FIG. 20 exemplarily shows PDCCH blocking for use in a concatenatedsearch space.

FIGS. 21 to 24 exemplarily show various methods for constructing aconcatenated search space according to another embodiment of the presentinvention.

FIG. 25 is a block diagram illustrating an eNode B and a user equipment(UE) applicable to the embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following embodiments ofthe present invention can be applied to a variety of wireless accesstechnologies, for example, CDMA, FDMA, TDMA, OFDMA, SC-FDMA, and thelike. CDMA can be implemented by wireless communication technologies,such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA canbe implemented by wireless communication technologies, for example,Global System for Mobile communications (GSM), General Packet RadioService (GPRS), Enhanced Data rates for GSM Evolution (EDGE), etc. OFDMAcan be implemented by wireless communication technologies, for example,IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (EvolvedUTRA), and the like. UTRA is a part of a Universal MobileTelecommunications System (UMTS). 3rd Generation Partnership Project(3GPP) Long Term Evolution (LTE) is a part of an Evolved UMTS (E-UMTS)that uses E-UTRA. In downlink, OFDMA is used. In uplink, SC-FDMA isused. LTE-Advanced (LTE-A) is an evolved version of 3GPP LTE.

Although the following embodiments of the present invention willhereinafter describe inventive technical characteristics on the basis ofthe 3GPP LTE/LTE-A system, it should be noted that the followingembodiments will be disclosed only for illustrative purposes and thescope and spirit of the present invention are not limited thereto.Specific terms used for the exemplary embodiments of the presentinvention are provided to aid in understanding of the present invention.These specific terms may be replaced with other terms within the scopeand spirit of the present invention.

FIG. 1 exemplarily shows a radio frame structure.

Referring to FIG. 1, a radio frame includes 10 subframes, and onesubframe includes two slots in a time domain. A time required fortransmitting one subframe is defined as a Transmission Time Interval(TTI). For example, one subframe may have a length of 1 ms and one slotmay have a length of 0.5 ms. One slot may include a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or a SingleCarrier Frequency Division Multiple Access (SC-FDMA) symbol in a timedomain. Since the LTE system uses OFDMA in downlink and uses SC-FDMA inuplink, the OFDM or SC-FDMA symbol indicates one symbol duration. Aresource block (RB) is a resource allocation unit and includes aplurality of contiguous carriers in one slot. The structure of the radioframe is only exemplary. Accordingly, the number of subframes includedin the radio frame, the number of slots included in the subframe or thenumber of symbols included in the slot may be changed in variousmanners.

FIG. 2 exemplarily shows a resource grid of a downlink slot.

Referring to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in a time domain. One downlink slot includes 7 (or 6) OFDMsymbols and a resource block (RB) includes 12 subcarriers in a frequencydomain. Each element on a resource grid may be defined as a resourceelement (RE). One RB includes 12×7 (or 12×6) REs. The number (N^(DL)) ofRBs contained in a downlink slot is dependent upon a downlinktransmission bandwidth. An uplink slot structure is identical to thedownlink slot structure, but OFDM symbols are replaced with SC-FDMAsymbols in the uplink slot structure differently from the downlink slotstructure.

FIG. 3 is a downlink subframe structure.

Referring to FIG. 3, a maximum of three (or four) OFDM symbols locatedin the front part of a first slot of the subframe may correspond to acontrol region to which a control channel is allocated. The remainingOFDM symbols correspond to a data region to which a Physical DownlinkShared Channel (PDSCH) is allocated. A variety of downlink controlchannels may be used in LTE, for example, a Physical Control FormatIndicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH),a Physical hybrid ARQ indicator Channel (PHICH), etc. PCFICH istransmitted from a first OFDM symbol of the subframe, and carriesinformation about the number of OFDM symbols used for transmitting acontrol channel within the subframe. PHICH carries a Hybrid AutomaticRepeat request acknowledgment/negative-acknowledgment (HARQ ACK/NACK)signal as a response to an uplink transmission signal.

Control information transmitted over a PDCCH is referred to as DownlinkControl Information (DCI). DCI includes resource allocation informationfor either a UE or a UE group and other control information. Forexample, DCI includes uplink/downlink (UL/DL) scheduling information, anuplink transmission (UL Tx) power control command, etc.

PDCCH carries a variety of information, for example, transmission formatand resource allocation information of a downlink shared channel(DL-SCH), transmission format and resource allocation information of anuplink shared channel (UL-SCH), paging information transmitted over apaging channel (PCH), system information transmitted over the DL-SCH,resource allocation information of an upper-layer control message suchas a random access response transmitted over PDSCH, a set of Tx powercontrol commands of each UE contained in a UE group, a Tx power controlcommand, activation indication information of Voice over IP (VoIP), andthe like. A plurality of PDCCHs may be transmitted within a controlregion. A user equipment (UE) can monitor a plurality of PDCCHs. PDCCHis transmitted as an aggregate of one or more contiguous control channelelements (CCEs). CCE is a logical allocation unit that is used toprovide a coding rate based on a radio channel state to a PDCCH. CCE maycorrespond to a plurality of resource element groups (REGs). The formatof PDCCH and the number of PDCCH bits may be determined according to thenumber of CCEs. A base station (BS) decides a PDCCH format according toDCI to be sent to the UE, and adds a Cyclic Redundancy Check (CRC) tocontrol information. The CRC is masked with an identifier (e.g., RadioNetwork Temporary Identifier (RNTI)) according to a PDCCH owner or apurpose of the PDCCH. For example, provided that the PDCCH is providedfor a specific UE, an identifier of the corresponding UE (e.g.,cell-RNTI (C-RNTI)) may be masked with the CRC. If PDCCH is provided fora paging message, a paging identifier (e.g., paging-RNTI (P-RNTI)) maybe masked with a CRC. If PDCCH is provided for system information (e.g.,system information block (SIC)), system information RNTI (SI-RNTI) maybe masked with CRC. If PDCCH is provided for a random access response,random access-RNTI (RA-RNTI) may be masked with CRC. For example, CRCmasking (or scrambling) may perform an XOR operation between CRC andRNTI at a bit level.

PDCCH may carry a message known as a DCI. Generally, several PDCCHs maybe transmitted in a subframe. Each PDCCH is transmitted using one ormore CCEs. One CCE may be mapped to 9 REGs, and one REG may be mapped tofour REs. Four QPSK symbols may be mapped to individual REGs. Resourceelements occupied by a reference signal (RS) are not contained in anREG. Therefore, the number of REGs for use in a given OFDM symbol ischanged according to the presence or absence of a cell-specificreference signal (RS). REG concept may also be applied to other downlinkcontrol channels (that is, PDFICH and PHICH). As can be seen from Table1, four PDCCH formats are supported.

TABLE 1 PDCCH Number of Number of Number of format CCEs (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are numbered so that the CCEs can be contiguously used. In order tosimplify the decoding process, a PDCCH having a format comprised of nCCEs may start from only a CCE having a specific number corresponding toa multiple of n. The number of CCEs used for transmission of a specificPDCCH may be determined by the eNode B according to a channel status.For example, in case of a PDCCH for a UE (for example, the UE mayneighbor the eNode B) having a good DL channel, only one CCE cansufficiently satisfy the PDCCH. However, in case of a PDCCH for a UEhaving a poor channel (for example, the UE may exist in the vicinity ofa cell edge), 8 CCEs may be requested to obtain sufficient robustness.In addition, a PDCCH power level may be adjusted in response to achannel status.

In the case of the LTE system, a CCE set in which a PDCCH may be locatedfor each UE may be defined. CCE set in which the UE can discover its ownPDCCH will hereinafter be referred to as a PDCCH search space or simplya search space (SS). Each resource through which a PDCCH can betransmitted within a search space (SS) is referred to as a PDCCHcandidate. One PDCCH candidate may correspond to 1, 2, 4 or 8 CCEsaccording to a CCE aggregation level. The eNode B transmits an actualPDCCH (DCI) to an arbitrary PDCCH candidate contained in the searchspace (SS), and the UE monitors the search space to search for a PDCCH(DCI). In more detail, the UE attempts to perform blind decoding (BD) ofPDCCH candidates contained in the search space (SS).

In the LTE system, the search spaces (SSs) for respective PDCCH formatsmay have different sizes. A dedicated (or UE-specific) search space (SS)and a common SS may be defined. The dedicated search space (SS) may beconfigured for each UE, and all UEs receive information regarding thecommon SS range. The dedicated or common SS may overlap with a given UE.

The search spaces (SSs) may be configured in small size and may overlapeach other, such that it may be impossible for the eNode B to search forCCE resources that transmit a PDCCH to all desired UEs within a givensubframe. That is, CCE resources have already been allocated to otherUEs, because CCE resources for the corresponding UE may no longer bepresent in a search space of the specific UE (i.e., blocking of CCEresources). In order to minimize the possibility of blocking to besustained in the next subframe, a UE-specific hopping sequence isapplied to the start position of the dedicated search space. Table 2shows the sizes of common and dedicated search spaces.

TABLE 2 Number of candi- Number of candi- PDCCH Number of dates incommon dates in dedicated format CCEs (n) search space search space 0 1— 6 1 2 — 6 2 4 4 2 3 8 2 2

In order to control calculation load (or operation load) caused by theblind decoding attempt, the UE does not simultaneously search for allthe defined DCI formats. Generally, the UE always searches for format 0and format 1A in the dedicated search space. Format 0 and format 1A havethe same size, and are distinguished from each other by a flag containedin a message. In addition, the UE may further request other formats(i.e., format 1, 1B or 2 according to PDSCH transmission modeestablished by the eNode B). The UE searches format 1A and format 1C inthe common search space. In addition, the UE may be configured to searchfor format 3 or 3A. Formats 3/3A have the same size in the same manneras in formats 0/1A, and are distinguished from each other according towhether a scrambled CRC is used as another (common) identifier.Transmission modes and DCI format contents to construct themulti-antenna technology are as follows.

Transmission Mode

-   -   Transmission Mode 1: Transmission from a single base station        antenna port    -   Transmission Mode 2: Transmit diversity    -   Transmission Mode 3: Open-loop spatial multiplexing    -   Transmission Mode 4: Closed-loop spatial multiplexing    -   Transmission Mode 5: Multi-user MIMO    -   Transmission Mode 6: Closed-loop rank-1 precoding    -   Transmission Mode 7: Transmission using UE-specific reference        signals

DCI Format

-   -   Format 0: Resource grants for PUSCH transmissions (uplink)    -   Format 1: Resource assignments for single codeword PDSCH        transmissions (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using rank-1        closed loop precoding (mode 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Format 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/1-bit power adjustments

FIG. 4 is a flowchart illustrating a method for constructing a PDCCH byan eNode B.

Referring to FIG. 4, the eNode B generates control information accordingto a DCI format. The eNode B may select one of a plurality of DCIformats (i.e., DCI formats 1, 2, . . . , N) according to types ofcontrol information to be transmitted to the UE. In step S410, the eNodeB attaches a cyclic redundancy check (CRC) for error detection tocontrol information that is generated according to each DCI format. TheCRC is masked with a Radio Network Temporary Identifier (RNTI) accordingto an owner or usage of the PDCCH. In other words, the PDCCH isCRC-scrambled with an identifier (e.g., RNTI).

Table 3 shows examples of identifiers masked to the PDCCH.

TABLE 3 Type Identifier Description UE-specific C-RNTI, used for aunique UE identification temporary C-RNTI, semi-persistent C-RNTI CommonP-RNTI used for paging message SI-RNTI used for system informationRA-RNTI used for random access response

If a C-RNTI, a temporary C-RNTI or a semi-persistent C-RNTI is used, thePDCCH carries UE-specific control information and, if another RNTI isused, the PDCCH carries common control information received by all UEswithin a cell. In step S420, the control information to which the CRC isattached is subjected to channel coding so as to generate coded data. Instep S430, rate matching according to a CCE aggregation level allocatedto a PDCCH format is performed. In step S440, the coded data ismodulated so as to generate modulated symbols. The modulated symbolsconfiguring one PDCCH may have one of CCE aggregation levels of 1, 2, 4and 8. In step S450, the modulated symbols (CCEs) are mapped to REs.

FIG. 5 is a flowchart illustrating a method of processing a PDCCH at aUE.

Referring to FIG. 5, in step S510, the UE demaps physical REs to CCEs.In step S520, since the UE is not aware of a CCE aggregation level, atwhich the UE receives a PDCCH, demodulation is performed with respect tothe CCE aggregation levels. In step S530, the UE performs ratedematching with respect to the demodulated data. Since the UE is notaware of a DCI format (or a DCI payload size) of control information tobe received, rate dematching is performed with respect to each DCIformat (or each DCI payload size). In step S540, the data subjected torate dematching is subjected to channel decoding according to a coderate and a CRC is checked to detect whether errors occur. If errors donot occur, it is determined that the UE detects a PDCCH thereof. Iferrors occur, the UE continues to perform BD with respect to other CCEaggregation levels or other DCI formats (or DCI payload sizes). In stepS550, the UE which detects the PDCCH removes the CRC from the decodeddata and acquires control information.

A plurality of PDCCHs for a plurality of UEs may be transmitted within acontrol region of the same subframe. An eNode B does not provide a UEwith information about the position of a PDCCH in the control region.Accordingly, the UE monitors a set of PDCCH candidates and finds a PDCCHthereof. Monitoring refers to attempts to decode the received PDCCHcandidates at the UE according to DCI formats. This is referred to asblind decoding (blind detection). Through blind decoding, the UEidentifies the PDCCH transmitted thereto and, at the same time, decodesthe control information transmitted through the PDCCH. For example, inthe case in which the PDCCH is demarked with a C-RNTI, the UE may detectthe PDCCH when CRC errors do not occur.

In order to reduce overhead of blind decoding, the number of DCI formatsis defined to be less than the number of kinds of control informationtransmitted using the PDCCH. The DCI information includes a plurality ofdifferent information fields. The kind of each information field, thenumber of information fields, the bit number of each information field,etc. are changed according to DCI format. In addition, the size of thecontrol information matching the DCI format is changed according to DCIformat. An arbitrary DCI format may be used to transmit two or morekinds of control information.

Table 4 shows an example of control information transmitted in DCIformat 0. In the following description, the bit size of each informationfield is only exemplary and is not limited thereto.

TABLE 4 Information Field bit(s) (1) Flag for format0/format1A differen-1 tiation (2) Hopping flag 1 (3) Resource block assignment and hop-┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL) + 1)/2)┐ ping resource Allocation (4)Modulation and coding scheme and 5 redundancy Version (5) New dataindicator 1 (6) TPC command for scheduled PUSCH 2 (7) Cyclic shift forDM RS 3 (8) UL index (TDD) 2 (9) CQI request 1

The flag field is an information field for distinguishing between format0 and format 1A. That is, DCI format 0 and 1A have the same payload sizeand are distinguished by the flag field. The bit size of the resourceblock allocation and hopping resource allocation field may be changedaccording to a hopping PUSCH or a non-hopping PUSCH. The resource blockallocation and hopping resource allocation field for the non-hoppingPUSCH provides ┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐ bits to resourceallocation of a first slot within an uplink subframe. Here, N_(RB) ^(UL)is the number of resource blocks included in an uplink slot and dependson an uplink transmission bandwidth set in a cell. Accordingly, thepayload size of DCI format 0 may be changed according to uplinkbandwidth. DCI format 1A includes an information field for PDSCHallocation and the payload size of DCI format 1A may also be changedaccording to downlink bandwidth. DCI format 1A provides a referenceinformation bit size for DCI format 0. Accordingly, if the number ofinformation bits of DCI format 0 is less than the number of informationbits of DCI format 1A, “0” is added to DCI format 0 until the payloadsize of DCI format 0 becomes equal to the payload size of DCI format 1A.The added “0” is filled in a padding field of the DCI format.

FIG. 6 is a diagram showing the structure of an uplink subframe used inLTE.

Referring to FIG. 6, the uplink subframe includes a plurality of slots(e.g., two). The number of SC-FDMA symbols included in one slot may bechanged according to the length of a CP. For example, in the case of thenormal CP, the slot may include seven SC-FDMA symbols. The uplinksubframe is divided into a data region and a control region in afrequency domain. The data region includes a PUSCH and is used totransmit a data signal such as voice data. The control region includes aPUCCH and is used to transmit control information. The PUCCH includes RBpairs (e.g., m=0, 1, 2, 3) located at both ends of the data region on afrequency axis and hops between slots. The control information includesHARQ ACK/NACK, channel quality information (CQI), precoding matrixindicator (PMI), rank indication (RI), etc.

FIG. 7 is a diagram showing a carrier aggregation (CA) communicationsystem.

Referring to FIG. 7, a plurality of uplink/downlink Component Carriers(CCs) may be aggregated so as to support a wider uplink/downlinkbandwidth. The term “CC” may be replaced with other equivalent terms(e.g., carrier, cell and the like). The CCs may be contiguous ornon-contiguous in a frequency domain. The bandwidths of the CCs areindependently set. Asymmetric CA in which the number of UL CCs and thenumber of DL CCs are different is also possible. The control informationmay be set to be transmitted/received only through a specific CC. Such aspecific CC may be referred to as a primary CC and the remaining CCs maybe referred to as secondary CCs.

For example, if cross-carrier scheduling (or cross-CC scheduling) isapplied, a PDCCH for downlink allocation may be transmitted through DLCC#0 and a corresponding PDSCH may be transmitted through DL CC#2. Forcross-carrier scheduling, a carrier indicator field (CIF) is used.Setting presence/absence of the CIF in the PDCCH may be enabled throughhigher layer signaling (e.g., RRC signaling) in a semi-static andUE-specific (or UE-group-specific) manner. The basic matters (baselines)of PDCCH transmission are summarized as follows.

-   -   CIF disabled: A PDCCH on a DL CC is allocated PDSCH resources on        the same DL CC and PUSCH resources on a single linked UL CC.    -   No CIF    -   Identical to LTE PDCCH structure (same coding, same CCE-based        resource mapping) and DCI format    -   CIF enabled: A PDCCH on a DL CC may be allocated PDSCH or PUSCH        resources on one of a plurality of aggregated DL/UL CCs using a        CIF.    -   LTE DCI format extended to have a CIF    -   CIF (if set) is a fixed x-bit field (e.g., x=3)    -   The position of the CIF (if set) may be fixed regardless of a        DCI format size.    -   LTE PDCCH structure is reused (same coding, same CCE-based        resource mapping)

If the CIF is present, an eNode B may allocate a monitoring DL CC set inorder to reduce BD complexity of a UE. A PDCCH monitoring DL CC set is apart of all the aggregated DL CCs and includes one or more DL CCs, and aUE may detect/decode a PDCCH only in a corresponding DL CC. In otherwords, if the eNode B performs PDSCH/PUSCH scheduling, the PDCCH istransmitted only through the PDCCH monitoring DL CC set. The PDCCHmonitoring DL CC set may be set in a UE-specific, UE-group-specific orcell-specific manner. The term “PDCCH monitoring DL CC” may be replacedwith equivalent terms “monitoring carrier”, “monitoring cell”, etc. Inaddition, the term “aggregated CC” for a UE may be replaced with termssuch as “serving CC”, “serving carrier”, “serving cell”, etc.

FIG. 8 illustrates scheduling when a plurality of carriers isaggregated. It is assumed that 3 DL CCs are aggregated and DL CC A isset to a PDCCH monitoring DL CC. DL CC A, DL CC B and DL CC C may becalled serving CCs, serving carriers, serving cells, etc. In case of CIFdisabled, each DL CC may transmit only a PDCCH that schedules a PDSCHcorresponding to the DL CC without a CIF. When the CIF is enabledaccording to UE-specific (or UE-group-specific or cell-specific) higherlayer signaling, DL CC A (monitoring DL CC) may transmit not only aPDCCH that schedules the PDSCH corresponding to the DL CC A but alsoPDCCHs that schedule PDSCHs of other DL CCs. In this case, no PDCCH istransmitted in DL CC B and DL CC C not established as PDCCH monitoringDL CCs. Therefore, DL CC A (monitoring DL CC) must include all of aPDCCH search space related to DL CC A, a PDCCH search space related toDL CC B, and a PDCCH search space related to DL CC C. According to theembodiments of the present invention, it is assumed that the PDCCHsearch space is defined per carrier.

As described above, LTE-A considers utilizing the CIF in a PDCCH forcross-CC scheduling. Information as to whether the CIF is used (i.e.,support of a cross-CC scheduling mode or a non-cross-CC scheduling mode)and switching between modes may be semi-statically or UE-specificallyestablished through RRC signaling. After performing the correspondingRRC signaling process, the UE may recognize whether the CIF is used in aPDCCH to be scheduled in the UE.

FIG. 9 exemplarily shows eNB and UE operations for use in a CIFreconfiguration section. FIG. 9 assumes a reconfiguration situation inwhich the CIF is first switched off and then switched on.

Referring to FIG. 9, the eNode B transmits an RRC command (e.g.,“RRCConnectionReconfiguration” command), that transmits a CIFreconfiguration message to the corresponding UE, to the UE, such thatthe eNode B can establish information as to whether the CIF is used in aPDCCH into the corresponding UE (Step S904).

The UE transmits the received RRC command to its own RRC layer. Uponreceiving the RRC command from the eNode B, the UE transmits an RRCresponse message (e.g., “RRCConnectionReconfigurationComplete” message)carrying the CIF reconfiguration complete message to the eNode B throughthe RRC layer (Step S904).

Meanwhile, in the RRC signaling section 910 (

), a start time at which CIF reconfiguration (i.e., CIF on/off) startsmay be different between the eNB and the UE, such that there is littlepossibility of generating an unexpected error or malfunction not only inthe eNB PDCCH transmission but also in the UE reception/decodingprocess. In other words, there is a possibility that the eNB and the UEmat differently recognize whether the CIF is used in the same PDCCH at aspecific time point of the RRC signaling section 910. For example, theeNB may transmit a PDCCH without using the CIF, and the eNB mayreceive/decode the corresponding PDCCH using the CIF. In addition, theeNB transmits a PDCCH after inserting the CIF, and the UE mayreceive/decode the corresponding PDCCH without using the CIF. Suchmalfunction may cause unnecessary overhead in PDCCHtransmission/reception between the eNB and the UE, and may also increasea scheduling time delay.

Under the condition that multiple CCs are aggregated and cross-carrierscheduling is performed, a method for efficiently allocating a controlchannel and a method for constructing a search space will hereinafter bedescribed in detail. Prior to describing the following description, itshould be noted that transmission modes for use in aggregated CCs may beestablished independently of each other, and a bandwidth is allocated toeach CC, such that the same or different bandwidths may be used. Fromamong all the aggregated CCs for each UE (group), one or more DL CCs maybe established as a PDCCH monitoring DL CC for the corresponding UE(group). In addition, similarly to the legacy LTE, the present inventionassumes that BD for two DCI formats can be carried out in each PDCCHcandidate, the scope or spirit of the present invention is not limitedthereto. If necessary, BD for either at least one DCI format or at leastthree DCI formats for each PDCCH candidate can be carried out in eachPDCCH candidate.

Embodiment 1: Method for solving Ambiguity of Detected Control Channel

In LTE-A, a method for employing the CIF in a PDCCH so as to performcross-CC scheduling using aggregated CCs has been used. However, inorder to prevent the increase of additional blind decoding (BD) of a DCIformat size added by both backward compatibility with legacy LTE UEs andthe use of CIF, a method for disusing the CIF in a common SS has beenused.

On the other hand, a DCI format (hereinafter referred to as DCI formatA) having no CIF established in a common SS on a single DL CC may havethe same size as a DCI format (hereinafter referred to as DCI format B)that employs a CIF established in a UE-specific SS. A DCI format sizerefers to a DCI (payload) size. The DCI (payload) size may or may notinclude a CRC size according to definition. For example, the DCI formatsize may be changed according to a frequency band of a CC. DCI format Aand DCI format B may have the same or different formats. For convenienceof description, the above-mentioned DCI formats A/B will hereinafter bereferred to as the same-size DCI format (or the same-size DCI format orthe same size DCI) between SSs. Preferably, the present invention may belimited to the case in which the same-size DCI formats may be CRC-masked(or scrambled) using the same RNTI. For convenience of description, itis assumed that a CRC for use in the same-size DCI format is masked (orscrambled) with the same RNTI.

Meanwhile, under the condition that a common SS and a UE-specific SS areoverlapped with each other due to a certain reason (for example, SSallocation rule, SS hopping rule, etc.) and the same-size DCI formatsucceeds in DCI format decoding in the overlap region, the UE cannotdiscriminate which SS schedules the successfully-decoded PDCCH (i.e.,the UE cannot discriminate between a PDCCH including the CIF and a PDCCHhaving no CIF).

Various methods for solving the above-mentioned problems willhereinafter be described with reference to the attached drawings.Although the following description exemplarily shows that a common SS(no CIF) overlaps a UE-specific SS (CIF), the present invention may begeneralized in an exemplary case in which an SS including no CIFoverlaps an SS equipped with a CIF.

Method 1-1: Search Space Shift

In Method 1-1, under the condition that a common SS not utilizing theCIF and a UE-specific SS utilizing the CIF have the same DCI formatsize, and the common SS and the UE-specific SS are overlapped with eachother according to the predefined SS allocation/hopping rules, a methodfor shifting a UE-specific SS so as not to generate the overlap regionis proposed in Method 1-1. Preferably, the same-size DCI format may beCRC-scrambled with the same RNTI.

FIGS. 10A to 10D exemplarily show that a UE-specific SS is shifted atfour CCE aggregation levels (L=1, 2, 4, 8). In FIGS. 10A to 10D, CCE maybe limited to a CCE capable of being used as a PDCCH candidate in thecorresponding CCE aggregation level.

Referring to FIGS. 10A to 10D, an overlap region between the common SSand the UE-specific SS may occur at the left or right side on the basisof the common SS. Since the UE-specific SS is shifted, the overlapregion is prevented from being generated. As shown in FIGS. 10A to 10D,the UE-specific SS may move in the direction for minimizing the numberof shifted CCEs. The shift size (i.e., the number of CCEs) may be aminimum number of CCEs (or a predetermined value may also be added tothe minimum number of CCEs) for preventing the occurrence of the overlapregion. On the other hand, assuming that the number of shifted CCEs isidentical in both directions of the common SS as shown in FIG. 10C(L=4), the UE-specific SS may move in a predetermined direction (e.g.,to the right). The number of shifted CCEs may be determined inconsideration of only CCEs capable of being used as PDCCH candidates inthe corresponding CCE aggregation level.

In another method, a shift direction of the UE-specific SS and thenumber of shifted CCEs may be predetermined between the eNB and the UE,regardless of the position/size of the overlap region. For example, theshift direction of the UE-specific SS may be determined to be the rightdirection (or left direction) or may be close to a common SS boundary.In addition, the number of shifted CCEs may be identical to or higherthan a total number of CCEs (e.g., 16 CCEs) of a common SS. In thiscase, the shift direction of the UE-specific SS and the number ofshifted CCEs may be promised between the eNB and the UE, or may bedetermined by the eNB through signaling. In addition, some informationmay be predetermined, and the remaining information may be indicatedthrough signaling. Such signaling for the above-mentioned operation maybe carried out using RRC signaling or L1/L2 signaling (e.g., MACsignaling, PDCCH, etc.)

The above-mentioned description shows that all of the UE-specific SSsare shifted, under the condition that DCI formats established in thecommon SS (including no CIF) and the UE-specific SS (including CIF) areidentical in size and the common SS overlaps the UE-specific SS.However, the present invention may also apply the above-mentioned methodonly to a UE-specific SS region of a specific part actually overlappedwith the common SS, instead of to the entire UE-specific SS.

Method 1-2: Limiting Search Space Start Point

Method 1-2 provides, under the condition that a DCI format sizeestablished in a common SS not utilizing a CIF is identical to a DCIformat size established in a UE-specific SS utilizing the CIF, a methodfor establishing a start point (i.e., start CCE) of the UE-specific SSso as to prevent an overlap region from occurring between two SSs.

FIG. 11 exemplarily shows a method for limiting a start point of aUE-specific SS at each of four CCE aggregation levels (Ls) (where L=1,2, 4, 8). The common SS assumes that the CCE aggregation level is set to4 or 8. A total number of CCEs constructing a PDCCH candidate at eachCCE aggregation level (L) of the UE-specific SS is denoted by M_(L).

Referring to FIG. 11, if a DCI format size of the common SS (includingno CIF) is identical to that of the UE-specific SS (including CIF), andif the DCI format is preferably CRC-scrambled with the same RNTI, CCEs(16 CCEs) contained in the common SS and the last (M_(L)-1) CCEs locatedon CCE indexes are not allocated to the start points of thecorresponding UE-specific SS. In this case, CCE may be limited to CCEscapable of being used as a PDCCH candidate at the corresponding CCEaggregation level. For convenience of description, it is assumed thatthe M_(L) value for constructing the UE-specific SS in LTE is usedwithout change. In LTE, numbers of PDCCH candidates at L=1, 2, 4, 8 arerespectively set to 6, 6, 2, 2, resulting in M_(L)=6, 12, 8, 16. If thestart point of the UE-specific SS is established by the proposed method,no overlap region occurs between two SSs CRC-scrambled with the sameRNTI.

Method 1-1 or 1-2 is not limited to the case in which the DCI formatsize of the common SS is identical to that of the UE-specific SS. Inorder to protect the limited common SS region, it is possible to preventan overlap region from occurring between two SSs irrespective of the DCIformat size established in the two SSs. In addition, several UE-specificSSs for scheduling several CCs may be present in a single DL CC. If aDCI format size of a UE-specific SS not utilizing a CIF is identical tothat of a UE-specific SS utilizing the CIF and two SSs are overlappedwith each other, Method 1-2 may shift any one of UE-specific SS (e.g., aUE-specific SS utilizing the CIF) so as to prevent the occurrence of theoverlap region in a similar way to the proposed method, or may limit thestart point of any UE-specific SS so as to prevent the overlap regionfrom occurring between two SSs.

Method 1-3: Limitation of DCI Transmission

Method 1-3 proposes a method for limiting control channel (or DCI)transmission in a common SS and a UE for the same, under the conditionthat there is a possibility of causing ambiguity of a control channel(or control information) either in a common SS not utilizing a CIF or ina UE-specific SS utilizing the CIF.

FIG. 12 shows an example in which a network apparatus (e.g., eNB)transmits a control channel.

Referring to FIG. 12, the eNB configures a common SS and one or moreUE-specific SSs in step S1210. Each SS includes a set of control channelcandidates. SS configuration is carried out by a process for determiningcontrol channel allocation. The process for determining the controlchannel allocation may include a process for determining PDCCHallocation. By the process for determining PDCCH allocation, SS size(e.g., the number of CCEs), a CCE aggregation level of a PDCCHcandidate, the location of SS, etc. may be determined. In this example,a control channel candidate of the common SS does not include a CIFfield, and a control channel candidate of a UE-specific SS includes theCIF field. Each UE-specific SS is configured per CC. One controlinformation format may be established per DL CC or UL CC of the searchspace. Two or more control information formats may be established per DLCC or UL CC. In addition, DL/UL common control information format may beestablished in the search space in the same manner as in DCI formats0/1A of the LTE. The search space configuration scheme may be based onthe scheme for constructing the PDCCH search space of the legacy LTE.However, parameters (for example, hashing pattern, position, size, etc.)of the search space for each CC may be obtained by a combination of aparameter related to a PDCCH search space of the legacy LTE and a CIFvalue. In this example, a common SS and at least one UE-specific SS maybe received through the control region of the same subframe on the sameDL CC (for example, anchor CC (or PCC) or monitoring CC). The common SSmay overlap the UE-specific SS as necessary. The control channelincludes a PDCCH and the control channel candidate includes a PDCCHcandidate. The control channel carries a variety of control information,and a variety of control information formats may exist according tocontrol information types/contents.

Thereafter, the eNode B may transmit a control channel of a specific UEthrough a common SS and at least one UE-specific SS in step S1220. Inthis example, the common SS and at least one UE-specific SS may betransmitted through the same subframe on the same carrier. In moredetail, the common SS and at least one UE-specific SS may be transmittedthrough a control region (that is, a maximum of 3 (or 4) contiguous OFDMsymbols indicated by PCFICH) within the subframe. The control channel(or control information) may carry identification (ID) information toindicate the corresponding UE. The ID information may include RNTI(e.g., C-RNTI, SPS-RNTI, etc.). The control channel (or controlinformation) may be scrambled using such ID information. For example,the eNode B may transmit a PDCCH being CRC-scrambled with C-RNTI, to theUE. In this example, it is assumed that a control channel transmittedthrough a common SS and a control channel transmitted through theUE-specific SS are scrambled with the same RNTI.

On the other hand, there may be a possibility of causing ambiguity of acontrol channel (or control information) in each of the common SS andthe UE-specific SS. If there is a possibility of causing ambiguity ofthe control channel, the common SS may overlap the UE-specific SS due tothe SS allocation/hopping rules and the like. In addition, if there is apossibility of causing ambiguity of the control channel, a controlchannel candidate of the common SS (including no CIF) and a controlchannel candidate of the UE-specific SS (including CIF) have the sameDCI format size (that is, DCI payload size), and the control channelcandidates of two DDs may preferably have the same identifier (e.g.,RNTI) and/or the same first CCE resource. In this case, the commonsearch space according to Method 1-3 may limit control channel (or DCI)transmission in at least some parts of control channel candidates.

For example, if there is a possibility of causing ambiguity of a controlchannel in a common SS or a UE-specific SS, control channel (or DCI)transmission may be dropped from at least some parts of control channelcandidates in the common search space. A region for limiting controlchannel (or DCI) transmission may be the entire common search space,overlap region(s) of the common search space, or some parts (or controlchannel resources (e.g., CCE) corresponding to the above-mentionedregion) of such overlap regions. In this implementation example,limitation of control channel (or DCI) transmission may be achievedeither in the process for allocating control channel resources to a DCI,or in an actual transmission process. In addition, according to theimplementation example, limitation of control channel (or DCI)transmission may be achieved either through puncturing (or nulling)(i.e., a kind of rate matching) prior to resource mapping or throughpuncturing (or nulling) after such resource mapping. In summary, controlchannel (or DCI) transmission may be limited either in the case in whicha first control channel candidate to be monitored by the common SS and asecond control channel candidate to be monitored by the UE-specific SShave the same-size DCI format, or in the other case in which the firstand second control channel candidates have the same ID (e.g., RNTI)and/or the same start resource (e.g., start CCE).

FIG. 13 shows an example for processing a control channel (PDCCH) by aUE. Steps shown in FIG. 13 may correspond to those of FIG. 12, and assuch a detailed description thereof will refer to contents of FIG. 12.

Referring to FIG. 13, the UE receives a subframe including a controlregion in step S1310. The control region includes a common SS and atleast one UE-specific SS, and each SS includes a set of control channelcandidates. In this example, a control channel candidate of the commonSS does not include the CIF field and a control channel candidate of theUE-specific SS includes the CIF field. Each UE-specific SS is configuredper CC. Thereafter, in order to search for a control channel assigned tothe UE, the UE may determine the process for determining control channel(e.g., PDCCH) allocation in step S1320. The process for determiningcontrol channel allocation may include the process for monitoringcontrol channel candidates contained in the search space inconsideration of various parameters (e.g., the SS size (e.g., the numberof CCEs), a CCE aggregation level of the control channel candidate, theSS position, etc.) obtained by the predetermined rule in step S1320. Themonitoring process may include the process for performing blind decoding(BD) of each control channel candidate. Thereafter, the UE may carry outthe operations of a control channel assigned thereto in step S1330.

Meanwhile, there may be a possibility of causing ambiguity in a controlchannel (or control information) between the common SS and theUE-specific SS. In the case of constructing the SS under the conditionthat the possibility of causing ambiguity of a control channel exists,the common SS may overlap the UE-specific SS due to the SSallocation/hopping rules, etc. In addition, under the condition that thepossibility of causing ambiguity of a control channel exists, a controlchannel candidate of the common SS (including no CIF) and a controlchannel candidate of the UE-specific SS (including CIF) have the sameDCI format size (in other words, DCI payload size), and the controlchannel candidates of the two SSs may preferably include the same ID (orRNTI) and/or the same first CCE resource. In this case, according tothis method, it is assumed that the UE limits control channel (or DCI)transmission in at least some of control channel candidates of thecommon search space. Under the above-mentioned assumption, the UE mayperform the process for determining control channel allocation (morespecifically, the monitoring process). In other words, the UE mayperform the monitoring process on the assumption that a control channel(or DCI) is transmitted in a region for limiting control channel (DCI)transmission. The control channel (or DCI) transmission limitationregion may be the entirety of a common search space, overlap regions ofthe common search space, or some parts (or control channel resource(e.g., CCE) corresponding to the above-mentioned region) of the overlapregions. In brief, the above-mentioned assumption of control channel (orDCI) transmission limitation may be achieved either in the case in whicha first control channel candidate to be monitored by the common SS or asecond control channel candidate to be monitored by the UE-specific SSmay have the same-size DCI format, or in the other case in which thefirst and second control channel candidates may have the same ID (e.g.,RNTI) and/or the same start resource (e.g., the same start CCE).

In the present invention, according to the implementation example, theUE may search for only a DCI format of the UE-specific SS in atransmission limitation region of the control channel (or DCI). Forexample, the UE may search for only one of the same-size DCI formats ina specific SS region of a specific time point. In other words, if thesame DCI format size is established in two SSs, the UE may not performthe monitoring/BD process of the same-size DCI format established in thecommon SS of a specific SS region of a specific time point. In addition,according to the implementation example, it is assumed that the UEmonitors both the common SS and the UE-specific SS according to theconventional procedure and then receives the corresponding PDCCH at theUE-specific SS under the condition that a control channel (e.g., PDCCH)is detected in a control channel (or DCI) transmission limitationregion.

In order to limit transmission of the same-size DCI format in the commonSS, the following three methods may be considered. For convenience ofdescription, the same-size DCI format established in the common SS isreferred to as DCI_css, and the same-size DCI format established in theUE-specific SS is referred to as DCI_uss. ‘DCI css’ may include DCIformat 0 and DCI format 1A, each of which does not include a CIF of the3GPP LTE system.

Case 1) Case 1 that is applied only to the overlapped common SS regionwhen the overlap region occurs between two SSs

The eNode B does not transmit DCI_css only to the overlap region at aspecific time at which the overlap region occurs between the common SSand the UE-specific SS. FIG. 14A exemplarily shows the search spacestructure according to one embodiment of the present invention.Therefore, it is assumed that the UE transmits a control channel in theoverlap region only through the UE-specific SS. That is, if the controlchannel (or UCI) is detected in the overlap region, the UE considersthat the corresponding control channel is received in the UE-specificSS. In accordance with the implementation example, in association withthe same-size DCI formats at the corresponding time point, the UE mayperform reception/BD of DCI through the overlap region, and may performreception/BD of DCI_css through a common SS other than the overlapregion. In other words, the UE may not monitor a control channelcandidate for DCI_css in the overlap region. In another example, the UEmonitors all control channel candidates for DCI_css and DCI_uss in theoverlap region. If a control channel is detected, the detected controlchannel is considered to be DCIuss. The above-mentioned method of thepresent invention can allocate DCI_css to the common SS other than theoverlap region, such that scheduling flexibility reduction in the commonSS can be minimized.

Preferably, the present invention can limit transmission of the controlchannel candidates in the common SS only when a control channelcandidate of the common SS and a control channel candidate of theUE-specific SS have the same DCI (payload) size, the same RNTI (e.g.,CRC-scrambled) and the same start resource (e.g., CCE) in the overlapregion. FIG. 14B exemplarily shows a search space configuration andcontrol channel candidate transmission according to one embodiment ofthe present invention.

Case 2) Case 2 that is applied to the entire common SS region whenoverlap region occurs between two SSs

The eNB does not transmit DCI_css to the entire common SS region only ata time point at which the overlap occurs between the common SS and theUE-specific SS. Therefore, it is assumed that, if the overlap regionoccurs, a control channel is transmitted only in the overlap regionthrough the UE-specific SS. That is, it is assumed that, if a controlchannel is detected in the overlap region, the corresponding controlchannel is received in the UE-specific SS. In accordance with theimplementation example, in association with the same-size DCI formats atthe corresponding time point, the UE cannot perform reception/BD ofDCI_css through the entire common SS, and can perform reception/BD ofDCI_uss through the overlap region. In another example, the UE monitorsall control channel candidates for DCI_css and DCI_uss in the overlapregion. If a control channel is detected, the detected control channelis considered to be DCI_uss. While the above-mentioned method canfurther reduce scheduling flexibility in the common SS, it can reducecomplexity needed when the overlap region and the non-overlap region aredistinguished from each other.

Preferably, the present invention can limit control channel candidatetransmission in the entire common SS by monitoring control channelcandidates including the same DCI (payload) size, the same RNTI (e.g.CRC-scrambled) and the same start resource (e.g., CCE) in the common SSand the UE-specific SS.

Case 3) Case 3 that is applied to the entire common SS regionirrespective of the presence or absence of the overlap region

Irrespective of the presence or absence of the overlap region betweentwo SSs, DCI_css is not transmitted to the entire common SS region.Therefore, in association with the same-size DCI formats in the entireperiod of the cross-CC scheduling mode, the UE cannot performreception/BD of DCI_css through the entire common SS whereas the UE canperform reception/BD of DCI_uss in the overlap region. Overlap ornon-overlap of the SS is changed per subframe, such that reduction ofunnecessary scheduling flexibility is added even in the case in whichthe SS is not overlapped, and complexity needed when overlap ornon-overlap must be checked per subframe can be greatly reduced. Inanother example, if there is a possibility of causing ambiguity in acontrol channel (or control information) between the common SS notutilizing a CIF and the UE-specific SS utilizing the CIF, a method forlimiting control channel (or DCI) transmission in the UE-specific SS andUE operations for the same are proposed.

FIG. 16 shows an example in which the network device (e.g., eNB)transmits a control channel.

Referring to FIG. 16, the eNB configures a common SS and one or moreUE-specific SSs in step S1610. Each SS includes a set of control channelcandidates. SS configuration is carried out by a process for determiningcontrol channel allocation. The process for determining the controlchannel allocation may include a process for determining PDCCHallocation. By the process for determining PDCCH allocation, SS size(e.g., the number of CCEs), a CCE aggregation level of a PDCCHcandidate, the location of SS, etc. may be determined. In this example,a control channel candidate of the common SS does not include a CIFfield, and a control channel candidate of a UE-specific SS includes theCIF field. Each UE-specific SS is configured per CC. One controlinformation format may be established per DL CC or UL CC of the searchspace. Two or more control information formats may be established per DLCC or UL CC. In addition, DL/UL common control information format may beestablished in the search space in the same manner as in DCI formats0/1A of the LTE. The search space configuration scheme may be based onthe scheme for constructing the PDCCH search space of the legacy LTE.However, parameters (for example, hashing pattern, position, size, etc.)of the search space for each CC may be obtained by a combination of aparameter related to a PDCCH search space of the legacy LTE and a CIFvalue. In this example, a common SS and at least one UE-specific SS maybe received through the control region of the same subframe on the sameDL CC. The common SS may overlap the UE-specific SS as necessary. Thecontrol channel includes a PDCCH and the control channel candidateincludes a PDCCH candidate. The control channel carries a variety ofcontrol information, and a variety of control information formats mayexist according to control information types/contents.

Thereafter, the eNode B may transmit a control channel of a specific UEthrough a common SS and at least one UE-specific SS in step S1620. Inthis example, the common SS and at least one UE-specific SS may betransmitted through the same subframe on the same carrier. In moredetail, the common SS and at least one UE-specific SS may be transmittedthrough a control region (that is, a maximum of 3 (or 4) contiguous OFDMsymbols indicated by PCFICH) within the subframe. The control channel(or control information) may carry identification (ID) information toindicate the corresponding UE. The ID information may include RNTI(e.g., C-RNTI, SPS-RNTI, etc.). The control channel (or controlinformation) may be scrambled using such ID information. For example,the eNode B may transmit a PDCCH CRC-scrambled with C-RNTI, to the UE.In this example, it is assumed that a control channel transmittedthrough a common SS and a control channel transmitted through theUE-specific SS are scrambled with the same RNTI.

On the other hand, there may be a possibility of causing ambiguity of acontrol channel (or control information) in each of the common SS andthe UE-specific SS. If there is a possibility of causing ambiguity ofthe control channel, the common SS may overlap the UE-specific SS due tothe SS allocation/hopping rules and the like. In addition, if there is apossibility of causing ambiguity of the control channel, a controlchannel candidate of the common SS (including no CIF) and a controlchannel candidate of the UE-specific SS (including CIF) have the sameDCI format size (that is, DCI payload size), and the control channelcandidates of two DDs may preferably have the same identifier (e.g.,RNTI) and/or the same first CCE resource. In this case, the commonsearch space according to Method 1-3 may limit control channel (or DCI)transmission in at least some parts of control channel candidates.

For example, if there is a possibility of causing ambiguity of a controlchannel in a common SS or a UE-specific SS, control channel (or DCI)transmission may be dropped from at least some parts of control channelcandidates in the UE-specific search space. A region for limitingcontrol channel (or DCI) transmission may be the entire common searchspace, overlap region(s) of the common search space, or some parts (orcontrol channel resources (e.g., CCE) corresponding to theabove-mentioned region) of such overlap regions. In this implementationexample, limitation of control channel (or DCI) transmission may beachieved either in the process of allocating control channel resourcesto a DCI, or in an actual transmission process. In addition, accordingto the implementation example, limitation of control channel (or DCI)transmission may be achieved either through puncturing (or nulling)(i.e., a kind of rate matching) prior to resource mapping or throughpuncturing (or nulling) after such resource mapping. In summary, controlchannel (or DCI) transmission may be limited either in the case in whicha first control channel candidate to be monitored by the common SS and asecond control channel candidate to be monitored by the UE-specific SShave the same-size DCI format, or in the other case in which the firstand second control channel candidates have the same ID (e.g., RNTI)and/or the same start resource (e.g., start CCE).

FIG. 17 shows an example for processing a control channel (PDCCH) by aUE. Steps shown in FIG. 17 may correspond to those of FIG. 16, and assuch a detailed description thereof will refer to contents of FIG. 16.

Referring to FIG. 17, the UE receives a subframe including a controlregion in step S1710. The control region includes a common SS and atleast one UE-specific SS, and each SS includes a set of control channelcandidates. In this example, a control channel candidate of the commonSS does not include the CIF field and a control channel candidate of theUE-specific SS includes the CIF field. Each UE-specific SS is configuredper CC. Thereafter, in order to search for a control channel assigned tothe UE, the UE may determine the process for determining control channel(e.g., PDCCH) allocation in step S1720. The process for determiningcontrol channel allocation may include the process for monitoringcontrol channel candidates contained in the search space inconsideration of various parameters (e.g., the SS size (e.g., the numberof CCEs), a CCE aggregation level of the control channel candidate, theSS position, etc.) obtained by the predetermined rule in step S1720. Themonitoring process may include the process for performing blind decoding(BD) of each control channel candidate. Thereafter, the UE may carry outthe operations of a control channel assigned thereto in step S1730.

Meanwhile, there may be a possibility of causing ambiguity in a controlchannel (or control information) between the common SS and theUE-specific SS. In the case of constructing the SS under the conditionthat the possibility of causing ambiguity of a control channel exists,the common SS may overlap the UE-specific SS due to the SSallocation/hopping rules, etc. In addition, under the condition that thepossibility of causing ambiguity of a control channel exists, a controlchannel candidate of the common SS (including no CIF) and a controlchannel candidate of the UE-specific SS (including CIF) have the sameDCI format size (in other words, DCI payload size), and the controlchannel candidates of the two SSs may preferably include the same ID (orRNTI) and/or the same first CCE resource. In this case, according tothis method, it is assumed that the UE limits control channel (or DCI)transmission in at least some of control channel candidates of thecommon search space. Under the above-mentioned assumption, the UE mayperform the process for determining control channel allocation (morespecifically, the monitoring process). In other words, the UE mayperform the monitoring process on the assumption that a control channel(or DCI) is transmitted only on the common search space, in a region forlimiting control channel (DCI) transmission. The control channel (orDCI) transmission limitation region may be the entirety of a commonsearch space, overlap regions of the common search space, or some parts(or control channel resource (e.g., CCE) corresponding to theabove-mentioned region) of the overlap regions. In brief, theabove-mentioned assumption of control channel (or DCI) transmissionlimitation may be achieved either in the case in which a first controlchannel candidate to be monitored by the common SS or a second controlchannel candidate to be monitored by the UE-specific SS may have thesame-size DCI format, or in the other case in which the first and secondcontrol channel candidates may have the same ID (e.g., RNTI) and/or thesame start resource (e.g., the same start CCE).

In the present invention, according to the implementation example, theUE may search for only a DCI format of the common SS in a transmissionlimitation region of the control channel (or DCI). For example, the UEmay search for only one of the same-size DCI formats in a specific SSregion of a specific time point. In other words, if the same DCI formatsize is established in two SSs, the UE may not perform the monitoring/BDprocess of the same-size DCI format established in the UE-specific SS ofa specific SS region of a specific time point. In addition, according tothe implementation example, it is assumed that the UE monitors both thecommon SS and the UE-specific SS according to the conventional procedureand then receives the corresponding PDCCH at the common SS under thecondition that a control channel (e.g., PDCCH) is detected in a controlchannel (or DCI) transmission limitation region.

In order to limit transmitting the same-size DCI format in theUE-specific SS, the following three methods may be considered. Forconvenience of description, the same-size DCI format established in thecommon SS is referred to as DCI_css, and the same-size DCI formatestablished in the UE-specific SS is referred to as DCI_uss. ‘DCI_css’may include DCI format 0 and DCI format 1A, each of which does notinclude a CIF of the 3GPP LTE system.

Case 1) Case 1 that is applied only to the overlapped UE-specific SSregion when the overlap region occurs between two SSs

The eNB does not transmit DCI_uss only to the overlap region at aspecific time at which the overlap region occurs between the common SSand the UE-specific SS. FIG. 18A exemplarily shows the search spacestructure according to one embodiment of the present invention.Therefore, it is assumed that the UE transmits a control channel in theoverlap region only through the common SS. That is, if the controlchannel (or UCI) is detected in the overlap region, the UE considersthat the corresponding control channel is received in the common SS. Inaccordance with the implementation example, in association with thesame-size DCI formats at the corresponding time point, the UE mayperform reception/BD of DCI_css through the overlap region, and mayperform reception/BD of DCI_uss through the UE-specific SS other thanthe overlap region. In other words, the UE may not monitor a controlchannel candidate for DCI_uss in the overlap region. In another example,the UE monitors all control channel candidates for DCI_css and DCI_ussin the overlap region. If a control channel is detected, the detectedcontrol channel is considered to be DCI_css. The above-mentioned methodof the present invention can allocate DCI_uss to the UE-specific SSother than the overlap region, such that the scheduling flexibilityreduction in the UE-specific SS can be minimized.

Preferably, the present invention can limit transmission of the controlchannel candidates in the common SS only when a control channelcandidate of the common SS and a control channel candidate of theUE-specific SS have the same DCI (payload) size, the same RNTI (e.g.,CRC-scrambled) and the same start resource (e.g., CCE) in the overlapregion. FIG. 18B exemplarily shows a search space configuration andcontrol channel candidate transmission according to one embodiment ofthe present invention.

Case 2) Case 2 that is applied to the entire common SS region when theoverlap region occurs between two SSs

The eNB does not transmit DCI_uss to the entire UE-specific SS regiononly at a time point at which the overlap occurs between the common SSand the UE-specific SS. Therefore, it is assumed that, if the overlapregion occurs, a control channel is transmitted only in the overlapregion through the common SS. That is, it is assumed that, if a controlchannel is detected in the overlap region, the corresponding controlchannel is received in the common SS. In accordance with theimplementation example, in association with the same-size DCI formats atthe corresponding time point, the UE cannot perform reception/BD ofDCI_uss through the entire UE-specific SS, and can perform reception/BDof DCI_css through the overlap region. In another example, the UEmonitors all control channel candidates for DCI_css and DCI_css in theoverlap region. If a control channel is detected, the detected controlchannel is considered to be DCI_css. While the above-mentioned methodcan further reduce scheduling flexibility in the UE-specific SS, it canreduce complexity needed when the overlap region and the non-overlapregion are distinguished from each other.

Preferably, the present invention can limit control channel candidatetransmission in the entire UE-specific SS by monitoring control channelcandidates including the same DCI (payload) size, the same RNTI (e.g.CRC-scrambled) and the same start resource (e.g., CCE) in the common SSand the UE-specific SS.

Meanwhile, due to misalignment between the eNB and the UE related torecognition information as to whether the CIF is used during the CIFreconfiguration section through RRC signaling under the condition thatmultiple CCs are aggregated, a malfunction or erroneous operation mayoccur in PDCCH transmission/reception. In order to prevent theabove-mentioned problem from being generated, there may be used a methodfor excluding the CIF from a PDCCH that schedules a specific CC (e.g.,anchor CC (or PCC), or PDCCH monitoring CCs) from among the aggregatedCCs, regardless of the cross-CC or non-cross-CC scheduling mode (i.e.,regardless of CIF on/off setting). Irrespective of CIF reconfiguration,the eNB can transmit data including no CIF to a PDCCH of a specific CC(e.g., anchor CC (or PCC) or PDCCH monitoring CCs). In this case,regardless of CIF reconfiguration, the UE may receive/decode a PDCCH onthe assumption that CIF does not exist in the corresponding CC at alltimes. Therefore, in association with scheduling of the corresponding CCduring the CIF reconfiguration section, erroneous PDCCHtransmission/reception operations can be prevented from being generatedbetween the eNB and the UE. In this case, the above-mentioned SS overlapproblem may be extended to the overlap problem between the UE-specificSS through which a DCI including no CIF is transmitted and the otherUE-specific SS through which a DCI including a CIF is transmitted.

Therefore, if the SS overlap problem is generalized, this SS overlapproblem may represent that a DCI format including no CIF (i.e., noCIF-DCI) and a DCI format (i.e., CIF-DCI) including a CIF have the samesize and SSs used for transmission of the corresponding DCI formats mayoverlap with each other. In this case, similar to the above-mentionedexample, the eNB may transmit only a DCI of a specific SS from amongoverlapped SSs in a specific time/region, and the UE may determine aDCI, that is decoded and CRC-passed through the specific time/region, tobe a DCI of the specific SS. A detailed description for theabove-mentioned operations is as follows.

A) Method a that is Applied Only to the Overlap Region Between SSs

A-1. Transmission of Only DCI Including CIF (i.e., CIF-DCI)

In the overlap region at a time point at which the overlap region occursbetween SSs, the eNB may transmit only the CIF-DCI from among thesame-size DCIs and may stop transmission of no CIF-DCI. In accordancewith the implementation example, transmission limitation of no CIF-DCImay be achieved either in the process for allocating CCE resources to noCIF-DCI or in the actual transmission step of no CIF-DCI. In addition,according to the implementation example, transmission stoppage of noCIF-DCI may be achieved either through puncturing (or nulling) (or akind of rate matching) prior to resource mapping or through puncturing(or nulling) after resource mapping. Preferably, the present inventionmay be limited to the case in which no CIF-DCI and the CIF-DCI carry thesame RNTI (e.g., CRC is scrambled with the same RNTI). Therefore, inassociation with the same-size DCIs at the corresponding time point, theUE may recognize a DCI (i.e., PDCCH) detected through the overlap regionas a CIF-DCI. For this purpose, according to the implementation example,the UE may perform reception/BD of only the CIF-DCI through the overlapregion at the corresponding time point. That is, the UE may not monitorthe control channel candidate for no CIF-DCI in the overlap region. Inanother example, the UE monitors control channel candidates of both noCIF-DCI and the CIF-DCI in the overlap region. If a PDCCH is detected,the detected PDCCH is recognized as CIF-DCI.

The present invention can be effectively applied to the overlap regionbetween the common SS (for PDCCH monitoring CC) through which no CIF-DCI(e.g., DCI format 0/1A) is transmitted and the UE-specific SS (for PDCCHnon-monitoring CC) through which the CIF-DCI is transmitted. DCI format0/1A of the PDCCH monitoring CC can be transmitted not only through thecommon SS but also through the UE-specific SS. Therefore, althoughtransmission of no CIF-DCI format 0/1A is limited in the overlap region,the corresponding DCI format 0/1A can be transmitted not only throughthe non-overlapped common SS region but also through the UE-specific SSfor the PDCCH monitoring CC. The present invention can also be appliedto the case in which the UE-specific SSs are overlapped with each otherwithout change. That is, under the condition that the UE-specific SSthrough which the CIF-DCI is transmitted overlaps the other UE-specificSS through which no CIF-DCI is transmitted and the CIF-DCI and noCIF-DCI have the same size (e.g., payload size), only CIF-DCItransmission may be allowed in the SS overlap region. More specifically,under the condition that two certain SSs overlap with each other withoutdistinction between the UE-specific SS and the common SS and CIF-DCI andno CIF-DCI have the same size, only CIF-DCI transmission may be allowed.The present invention may limit transmission of no CIF-DCI within theentire overlap region or may also limit transmission of no CIF-DCI onlywhen a PDCCH candidate for no CIF-DCI and a PDCCH candidate for CIF-DCIare composed of the same start CCEs within the overlap region.

A-2. Transmission of Only DCI Including no CIF (i.e., no CIF-DCI)

In the overlap region at a time point at which the overlap region occursbetween SSs, the eNB may transmit only no CIF-DCI from among thesame-size DCIs and may stop transmission of CIF-DCI. In accordance withthe implementation example, transmission limitation of CIF-DCI may beachieved either in the process for allocating CCE resources to CIF-DCIor in the actual transmission step of CIF-DCI. In addition, according tothe implementation example, transmission stoppage of CIF-DCI may beachieved either through puncturing (or nulling) (or a kind of ratematching) prior to resource mapping or through puncturing (or nulling)after resource mapping. Therefore, the UE may recognize the same sizeDCI detected in the overlap region as no CIF-DCI at the correspondingtime point. In addition, the UE may search for only no CIF-DCI in theoverlap region. That is, the UE may not perform monitoring/BD of theCIF-DCI in the overlap region. Preferably, the present invention may belimited to the case in which no CIF-DCI and CIF-DCI carry the same RNTI(e.g., CRC is scrambled with the same RNTI). The present invention canbe efficiently applied to the case in which a first SS (for anchor CC(or PCC) or PDCCH monitoring CC) through which no CIF-DCI considered forCIF reconfiguration is transmitted overlaps a second SS (for non-anchorCC (or PCC) or PDCCH non-monitoring CC) through which CIF-DCI istransmitted. The present invention can be applied not only to theoverlap region between the common SS (no CIF-DCI) and the UE-specific SS(CIF-DCI), but also to the overlap region between the UE-specific SS (noCIF-DCI) and the other UE-specific SS (CIF-DCI). There is a possibilitythat importance/frequency of data transmitted through the anchor CC (orPCC) or the PDCCH monitoring CC is higher than those of other CCs.Therefore, the above-mentioned method of the present invention may firstguarantee the degree of freedom of the scheduling related to the anchorCC (or PCC) or the PDCCH monitoring CC. More specifically, under thecondition that two certain SSs overlap with each other withoutdistinction between the UE-specific SS and the common SS, and CIF-DCIand no CIF-DCI have the same size, only transmission of no CIF-DCI maybe allowed. The present invention may limit transmission of CIF-DCIwithin the entire overlap region or may also limit transmission ofCIF-DCI only when a PDCCH candidate for no CIF-DCI and a PDCCH candidatefor CIF-DCI are composed of the same start CCEs within the overlapregion.

A-3. Method A-1 and Method A-2 May be Selectively Used According to SS

If the UE-specific SS of the CIF-DCI and the common SS of no CIF-DCIhave the same DCI size and overlap with each other, transmission of noCIF-DCI may be limited in the overlap region at the overlap time point.In addition, under the condition that the UE-specific SS of CIF-DCI andthe other UE-specific SS of no CIF-DCI have the same DCI size andoverlap with each other, CIF-DCI transmission may be limited in theoverlap region at the overlap time point. The present invention maylimit transmission of specific DCI in the entire overlap region, or maylimit transmission of a specific DCI only when a PDCCH candidate for noCIF-DCI and a PDCCH candidate for CIF-DCI are composed of the same startCCEs within the overlap region.

Method B) Method B is Applied Only to the Entirety of a Specific SSRegion When the Overlap Region Occurs Between SSs

B-1. Transmission of Only DCI Including CIF (i.e., CIF-DCI)

In each SS region at a time point at which the overlap region occursbetween SSs, the eNB may transmit only the CIF-DCI from among thesame-size DCIs and may stop transmission of no CIF-DCI. In more detail,the eNB may transmit the CIF-DCI through its own SS including theoverlap region, and the eNB may stop transmitting no CIF-DCI through itsown SS including the overlap region. Therefore, the UE may detect onlyCIF-DCI of the same-size DCIs at the corresponding time point.

B-2. Transmission of Only DCI Including No CIF (i.e., No CIF-DCI)

In each SS region at a time point at which the overlap region occursbetween SSs, the eNB may transmit only no CIF-DCI from among thesame-size DCIs, and may stop transmission of CIF-DCI. In more detail,the eNB may transmit no CIF-DCI through its own overall SS including theoverlap region, and the eNB may stop transmission of CIF-DCI through itsown overall SS including the overlap region. Therefore, the UE maydetect only no CIF-DCI in association with the same-size DCIs at thecorresponding time point.

B-3. Method B-1 and Method B-2 May be Selectively Used According to SS

If the UE-specific SS of CIF-DCI and the common SS of no CIF-DCI havethe same DCI size and overlap each other, the eNB may limit transmissionof no CIF-DCI within each SS region at the overlap time point. Inaddition, if the UE-specific SS of CIF-DCI and the other UE-specific SSof no CIF-DCI have the same size and overlap with each other, the eNBmay limit CIF-DCI transmission within each SS region at the overlap timepoint. The above-mentioned example exemplarily shows the case in whichselection information as to whether CIF-DCI or no CIF-DCI is to betransmitted at the SS overlap occurrence time is promised between theeNB and the UE. In contrast, selection information as to whether CIF-DCIor no CIF-DCI is to be transmitted at the SS overlap occurrence time maybe semi-statically established through higher layer signaling (e.g., RRCsignaling).

On the other hand, if the eNB maps a DCI to a specific CCE aggregationlevel and transmits the mapped result, a DCI codeword may be repeated inunits of a predetermined number of CCEs due to circular-buffercharacteristics. As a result, the corresponding DCI may be detected at aCCE aggregation level lower than the corresponding CCE aggregation levelduring the UE blind decoding (BD) process. Considering theabove-mentioned situation, in association with two SSs (e.g., the commonSS having no CIF and the UE-specific SS having CIF) having the same DCIformat size, the above-mentioned method can be applied not only to allCCE aggregation levels (e.g., L=1, 2, 4, 8) of the UE-specific SS, butalso to a specific CCE aggregation level (for example, L=4, 8) (e.g.,the same CCE aggregation level as that of the common SS). In otherwords, if the UE-specific SS has L=1 or L=2 and the overlap regionoccurs between the UE-specific SS and the common SS, the SS shiftingscheme, the SS start point limitation scheme, and the method forlimiting transmission of no CIF-DCI or CIF-DCI may not be used asnecessary.

In addition, in order to prevent the occurrence of ambiguity of the CCEaggregation level, if a DCI detected in a PDCCH candidate of the smallerCCE aggregation level (e.g., L=1 and/or L=2) and a DCI detected in aPDCCH candidate of the larger CCE aggregation level (e.g., L=4 and/orL=8) are simultaneously present in the CCE group starting from the sameCCE, the UE may discard the DCI detected in the smaller CCE aggregationlevel and may use only the DCI detected in the larger CCE aggregationlevel as control information. For example, if only CIF-DCI is supportedin the smaller CCE aggregation level and only no CIF-DCI is supported inthe larger CCE aggregation level, and if CRC-checked DCIs are present inboth the larger CCE aggregation level and the smaller CCE aggregationlevel, each CRC-checked DCI may be interpreted as the DCI (i.e., noCIF-DCI) of the larger CCE aggregation level. Alternatively, in order toobtain the same result, if the larger CCE aggregation level (e.g., L=4and/or L=8) is detected in the specific CCE group, the present inventionmay not attempt to detect the smaller CCE aggregation level (e.g., L=1and/or L=2) in the corresponding CCE group.

More specifically, the present invention may use the aforementionedproposed methods only when the SS having no CIF-DCI and the other SShaving CIF-DCI have the same CCE aggregation level and the same DCIsize, and then overlap with each other. If the SS having no CIF-DCI andthe SS having CIF-DCI have the same size and different CCE aggregationlevels, and overlap with each other, and if DCIs successfully detectedthrough PDCCH candidates of different CCE aggregation levels (i.e., highor low CCE aggregation levels) are simultaneously present in the CCEgroups starting from the same CCE, the UE may discard the DCI detectedin the smaller CCE aggregation level and may use only the DCI detectedin the larger CCE aggregation level as control information.Alternatively, in order to obtain the same result, if the larger CCEaggregation level is detected in the specific CCE group, the presentinvention may not attempt to detect the smaller CCE aggregation level inthe corresponding CCE group.

Embodiment 2: SS Allocation for Preventing Collision Between UE-SpecificSSs

LTE-A considers cross-CC scheduling using a CIF under the condition thatmultiple CCs are aggregated, such that it may be possible to transmitmultiple PDCCHs for scheduling multiple CCs through a single DL CC. Forthis purpose, a method for configuring multiple UE-specific SSs formultiple CCs in the corresponding DL CC may be used. IndividualUE-specific SSs may be classified according to individual CCs or DCIformat sizes. In this case, individual UE-specific SSs may haveindependent start CCE indexes and may be configured independent of eachother. Alternatively, multiple UE-specific SSs may have only one startpoint and may be configured to be concatenated. That is, multipleUE-specific SSs may be composed of concatenated SSs.

FIG. 20 exemplarily shows PDCCH blocking encountered in the concatenatedSS.

Referring to FIG. 20, if the allocation position or order of each SSconstructing the entire SSs within the concatenated SS is fixed in allsubframes, the overlap region may occur only between specific SSs. Theabove-mentioned example shows that four SSs on a single DL CC have asingle start point and a fixed SS order (#1→#2→#3→#4) and configures theconcatenated SS, such that it can be recognized that the overlap regionoccurs between SS #1 and SS #4 as can be seen from FIG. 20. In thisexample, for convenience of description, it is assumed that 6 PDCCHcandidates are allocated to each SS and a total number of CCEs may beset to 22. In this case, since specific SSs causing the overlap regionare fixed, the PDCCH scheduling freedom degree is reduced only in thecorresponding SSs (that is, the probability of PDCCH blocking isincreased). In this case, PDCCH blocking may indicate that PDCCHscheduling of the corresponding carrier is restricted due to the limitedPDCCH resources. In other words, as can be seen from FIG. 20, ifmultiple PDCCH search spaces are defined in one carrier, availableresources of the PDCCH search space corresponding to each carrier may belimited due to the limited PDCCH resources. As a result, the PDCCHallocation position may be limited or it may be impossible to performPDCCH allocation.

Although FIG. 20 shows that the concatenated SSs of one UE arewrap-around processed and overlap each other, the scope or spirit of thepresent invention is not limited thereto and such SS overlapping mayoccur due to a variety of reasons. For example, if the concatenated SSsof one UE are not wrap-around processed, and if the concatenated SS ofthe corresponding UE overlaps the concatenated SS of another UE, onlySSs of the specific CC overlap each other, such that only the SSs of thespecific CC may be intensively limited as necessary.

This embodiment of the present invention may propose a method forchanging the allocation order of each SS constructing the concatenatedSS. Each SS allocation order may be periodically changed (e.g., in unitsof each subframe). In this example, CCE may be limited only to a CCEcapable of being used as a PDCCH candidate in the corresponding CCEaggregation level.

The embodiments of the present invention will hereinafter be describedwith reference to FIGS. 21 to 24. Although individual SSs contained inthe concatenated SS are contiguous to each other in FIGS. 21 to 24, thescope or spirit of the present invention is not limited thereto, andindividual SSs contained in the concatenated SS may be configured atintervals of a specific offset configured in units of CCE or PDCCHcandidate or may overlap each other.

As can be seen from FIG. 21, a method for cyclically shifting the orderof each SS contained in the entire SS at intervals of a predeterminedtime (e.g., P subframes, P radio frames, or the like) may be used asnecessary. P may be an integer of more than 1. Preferably, P may be setto 1. The cyclic shift value may be changed at intervals of apredetermined time, and may be determined to be a function such as asubframe number, a system frame number (SFN) or the like. As a result,individual SSs, each of which has the overlap possibility, may beperiodically changed and allocated. Therefore, the probability of PDCCHblocking is not concentrated in a specific SS, and may be evenlydistributed to all individual SSs.

On the other hand, in order to prevent the occurrence of misalignmentbetween the eNB and the UE related to the SS location within the CIFreconfiguration section, the SS position of the anchor CC (or PCC)and/or the SS position of the PDCCH monitoring CC are always fixed inthe entire SS, and the allocation order of each SS other than the anchorCC (or PCC) and/or the PDCCH monitoring CC may be periodically changedin the remaining CCEs. Preferably, the SS position(s) of the anchor CC(or PCC) and/or the PDCCH monitoring CC may first be allocated to theCCE group having the lowest index from among all SSs.

In addition, the eNB configures the concatenated SS by applying theproposed method to N CCs regardless of CIF configuration (i.e., CIFon/off), and the UE may also perform blind decoding (BD) of only M CCs(where M≦N). In this case, N is a predetermined maximum number of CCs,the number of CCs deployed in a cell, or the number of CCs (e.g., thenumber of RRC-allocated UE-specific CCs, the number of cross-CCscheduled CCs from the corresponding PDCCH monitoring CC, and the like)semi-statically established in the corresponding UE. M may be set to thenumber of cross-CC scheduled CCs from the PDCCH monitoring CC accordingto CIF configuration, or may also be set to 1 (indicating only thecorresponding PDCCH monitoring CC).

In another method, after configuring each SS using the concept shown inFIG. 21, the SS start point(s) of the anchor CC (or PCC) and/or thePDCCH monitoring CC may be shifted to the start point of the entire SS.For example, as can be seen from FIG. 22, under the condition that theSS order is denoted by ‘2341’ and SS #1 is SS of the anchor CC (or PCC)and/or the PDCCH monitoring CC, the start point of SS #2 is set to thestart point of the entire SS such that all the SSs are configured, theentire SS (in which SS #1 and SS #2 overlap each other) is shifted insuch a manner that the start point of SS #1 is located at the startpoint of the entire SS, resulting in configuration of the last SS.Similar to FIG. 22, as can be seen from FIG. 23, after configuring SS #1in a manner that the start point of SS (SS #1) of the anchor CC (or PCC)and/or the PDCCH monitoring CC is identical to the start point of theentire SS, the remaining SSs (SS #2, #3, #4) may be concatenated in theleft and/or right direction of SS #1 according to the SS order,resulting in configuration of the concatenated SS.

The present invention performs random interleaving of all PDCCHcandidates of each SS in units of a PDCCH candidate, such that it canconfigure the concatenated SS. In more detail, the interleaving patternmay be randomized with a specific period (e.g., P subframes, P radioframes, and the like). P is an integer equal to or higher than 1.Preferably, P is set to 1 (P=1). However, it should be noted that thescope or spirit of the present invention is not limited thereto, and theinterleaving pattern for each period may be determined to be any one offunctions such as a subframe number, a system frame number (SFN), etc.In addition, an input/output (I/O) unit of the interleaver (i.e., a CCEaggregation level) may have a resolution of a PDCCH candidate. Forexample, if individual SSs are concatenated and input to theinterleaver, permutation is performed in units of a PDCCH candidateregardless of the order of individual SSs or the order of PDCCHcandidate, such that the permutation result is finally output.

FIG. 24 exemplarily shows interleaving of all PDCCH candidates ofindividual SSs. For convenience of description, the Y-th PDCCH candidatein the X-th SS (SS #X) is denoted by X-Y.

Referring to FIG. 24, PDCCH candidates corresponding to the same orderwithin individual SSs are collected and concatenated to each other, suchthat the concatenated SS can be configured. For convenience ofdescription and better understanding of the present invention, it isassumed that four SSs exist and 6 PDCCH candidates are present in eachSS. In this case, PDCCH candidates 1-1 to 1-4 selected from amongrespective SSs are concatenated in the region for PDCCH candidate #1.Similarly, the regions for PDCCH candidate #2 to PDCCH candidate #6 arealso configured, resulting in configuration of the concatenated SS inwhich PDCCH candidates #1˜#6 are concatenated. Although the regions forindividual PDCCH candidates #X (X=1˜6) are concatenated as shown in FIG.24, the concatenated regions are disclosed only for illustrativepurposes, and the scope or spirit of the present invention is notlimited thereto. If necessary, the concatenated regions may beconfigured at intervals of a specific offset configured in units ofeither the region CCE for each PDCCH candidate #X (X=1˜6) or a PDCCHcandidate, or may overlap with each other.

For convenience of description and better understanding of the presentinvention, PDCCH candidates located in the region for each PDCCHcandidate #X (where X=1˜6) are denoted by a PDCCH candidate group #X(where X=1˜6). The order of PDCCH candidates within each PDCCH candidategroup #X (X=1˜6) may be fixed in all subframes according to the order(#1→#2→#3→#4) of individual SSs as shown in the annexed drawings. Inaddition, the order of PDCCH candidates may be periodically changedwithin each PDCCH group #X (X=1˜6) as shown in FIG. 21. For example, theorder of PDCCH candidates may be cyclically shifted in units of asubframe within each PDCCH group #X (X=1˜6). In addition, the order ofconcatenated PDCCH candidates #X (X=1˜6) may also be periodicallychanged as shown in FIG. 21. Through the above-mentioned operation,PDCCH candidates capable of being overlapped with each other are notconcentrated in a specific SS and are distributed into all individualSSs, such that the probability of causing PDCCH blocking may be evenlydistributed into all individual SSs.

On the other hand, in order to prevent the occurrence of misalignmentbetween the eNB and the UE in association with the SS position duringthe CIF reconfiguration period, the SS configuration and position of theanchor CC (or PCC) and/or the PDCCH monitoring CC within the entire SSare always fixed in a manner that all PDCCH candidates are concatenated.And, for only individual SSs other than the anchor CC (or PCC) and/orthe PDCCH monitoring CC in association with the remaining CCEs, each SSin which PDCCH candidates are interleaved may be configured. Preferably,SS(s) of the anchor CC (or PCC) and/or the PDCCH monitoring CC may firstbe allocated to a CCE group having the lowest index from among all theSSs.

In addition, the eNB may configure the concatenated SSs by applying theproposed method to N CCs regardless of CIF configuration (i.e., CIFon/off), and the UE may also perform blind decoding (BD) of only M CCs(where M≦N). In this case, N is a predetermined maximum number of CCs,the number of CCs deployed in a cell, or the number of CCs (e.g., thenumber of RRC-allocated UE-specific CCs, the number of cross-CCscheduled CCs from the corresponding PDCCH monitoring CC, and the like)semi-statically established in the corresponding UE. M may be set to thenumber of cross-CC scheduled CCs from the PDCCH monitoring CC accordingto CIF configuration, or may also be set to 1 (indicating only thecorresponding PDCCH monitoring CC).

In addition, independent start CCE indexes are allocated to individualPDCCH candidate groups, such that SSs for individual PDCCH candidategroups may be configured independent of each other. In this case, SSsfor individual PDCCH candidate groups need not be concatenated.

On the other hand, the proposed method of the present invention may beapplied to all CCE aggregation levels (e.g., L=1, 2, 4, 8) withoutlimitation, or may also be applied to a specific CCE aggregation level(e.g., L=4 or 8). The specific CCE aggregation level indicates a CCEaggregation level in which the number of CCEs constructing the PDCCHcandidate is relatively high.

FIG. 25 is a block diagram illustrating an eNode B (eNB) and a UEapplicable to the embodiments of the present invention.

Referring to FIG. 25, the wireless communication system includes aneNode B (eNB) 110 (also denoted by ‘BS’) and a UE 120. The eNB 110includes a processor 112, a memory 114, and a radio frequency (RF) unit116. The processor 112 may be constructed to implement the proceduresand/or methods disclosed in the embodiments of the present invention.The memory 114 may be connected to a processor 112, and store variousinformation related to operations of the processor 112. The RF unit 116is connected to the processor 112, and transmits and/or receives RFsignals. The UE 120 includes a processor 122, a memory 124, and an RFunit 126. The processor 122 may be constructed to implement theprocedures and/or methods disclosed in the embodiments of the presentinvention. The memory 124 may be connected to a processor 122, and storevarious information related to operations of the processor 122. The RFunit 126 is connected to the processor 122, and transmits and/orreceives RF signals. The eNB 110 and/or the UE 120 may include a singleantenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predeterminedfashion. Each of the structural elements or features should beconsidered selectively unless specified otherwise. Each of thestructural elements or features may be carried out without beingcombined with other structural elements or features. Also, somestructural elements and/or features may be combined with one another toconstitute the embodiments of the present invention. The order ofoperations described in the embodiments of the present invention may bechanged. Some structural elements or features of one embodiment may beincluded in another embodiment, or may be replaced with correspondingstructural elements or features of another embodiment. Moreover, it willbe apparent that some claims referring to specific claims may becombined with other claims referring to the other claims other than thespecific claims to constitute the embodiment or add new claims by meansof amendment after the application is filed.

The embodiments of the present invention have been described based ondata transmission and reception between a BS (or eNB) and a UE. Aspecific operation which has been described as being performed by theeNB (or BS) may be performed by an upper node of the eNB (or BS) as thecase may be. In other words, it will be apparent that various operationsperformed for communication with the UE in the network which includes aplurality of network nodes along with the eNB (or BS) can be performedby the BS or network nodes other than the eNB (or BS). The eNB (or BS)may be replaced with terms such as fixed station, Node B, eNode B (eNB),and access point. Also, the term UE may be replaced with terms such asmobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, orcombinations thereof. If the embodiment according to the presentinvention is implemented by hardware, the embodiment of the presentinvention can be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a module, a procedure, or a function, which performsfunctions or operations as described above. Software code may be storedin a memory unit and then may be driven by a processor. The memory unitmay be located inside or outside the processor to transmit and receivedata to and from the processor through various well known means.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

Exemplary embodiments of the present invention can be applied towireless communication systems such as a UE, a relay node (RN), and aneNode B (eNB).

What is claimed is:
 1. A method for performing a procedure fordetermining control channel allocation for a control channel by a userequipment (UE) in a wireless communication system, the methodcomprising: monitoring a plurality of control channel candidates having,in a common search space and one or more UE-specific search spaces on aprimary component carrier, a same radio network temporary identifier(RNTI), a same payload size and a same first control channel element(CCE) index but a different set of information fields, wherein, if acarrier indicator field is configured for the UE, for the plurality ofcontrol channel candidates, only the control channel is received in thecommon search space on the primary component carrier.
 2. The method ofclaim 1, wherein the monitoring of the plurality of control channelcandidates is carried out assuming that the control channel is receivedonly in the common search space.
 3. The method of claim 1, wherein theplurality of control channel candidates are Cyclic Redundancy Check(CRC)-scrambled with the same RNTI.
 4. The method of claim 1, whereinthe payload size is a downlink control information (DCI) payload size.5. The method of claim 1, wherein the control channel is a physicaldownlink control channel (PDCCH), and a control channel candidate amongthe plurality of control channel candidates is a PDCCH candidate.
 6. Themethod of claim 1, further comprising receiving a subframe, wherein thesubframe includes the common search space and the one or moreUE-specific search spaces on the primary component carrier.
 7. Themethod of claim 1, further comprising performing operations indicated bythe control channel.
 8. A user equipment (UE) configured to determinecontrol channel allocation for a control channel in a wirelesscommunication system, the user equipment (UE) comprising: a radiofrequency (RF) unit; and a processor, wherein the processor isconfigured to monitor a plurality of control channel candidates having,in a common search space and one or more UE-specific search spaces on aprimary component carrier, a same radio network temporary identifier(RNTI), a same payload size and a same first control channel element(CCE) index but a different set of information fields, wherein, if acarrier indicator field is configured for the UE, for the plurality ofcontrol channel candidates, only the control channel is received in thecommon search space on the primary component carrier.
 9. The UE of claim8, wherein the monitoring of the plurality of control channel candidatesis carried out assuming that the control channel is received only in thecommon search space.
 10. The UE of claim 8, wherein the plurality ofcontrol channel candidates are Cyclic Redundancy Check (CRC)-scrambledwith the same RNTI.
 11. The UE of claim 8, wherein the payload size is adownlink control information (DCI) payload size.
 12. The UE of claim 8,wherein the control channel is a physical downlink control channel(PDCCH), and a control channel candidate among the plurality of controlchannel candidates is a PDCCH candidate.
 13. The UE of claim 8, whereinthe processor is configured to receive a subframe, and the subframeincludes the common search space and the one or more UE-specific searchspaces on the primary component carrier.
 14. The UE of claim 8, whereinthe processor is configured to perform operations indicated by thecontrol channel.